Obsessions are unwanted and disturbing thoughts, images, or impulses that come repeatedly and out of nowhere. Obsessions make the person feel very anxious and as though they are losing control ...or losing their mind. They often make the person think they must do things "just right." Common themes of obsessions are contamination, losing control, harm (to self or others), unwanted sexual thoughts, religious obsessions (not just religious thoughts), and perfectionism.

Lee Baer, PhD says in The Imp of the Mind:

"You are not so abnormal as you think. Every human being is visited from time to time by the Imp of the Perverse, who makes you think the most inappropriate thoughts at the most inappropriate times."

In a survey, for example, of normal college students almost all of them had one or more of these thoughts occasionally: